This invention relates to the treatment of dusts for the recovery of their metal value, and is more particularly concerned with the recovery of indium from lead and indium-containing dusts and lead from lead-containing dusts in a stirred bath of molten lead which contains dissolved sodium.
In the treatment of copper ores, zinc ores, or lead ores in a smelting operation, residues are produced, i.e., as flue ash or dust. Generally speaking, these dusts or residues can consist primarily of lead with lesser percentages of zinc and copper. Valuable by-products, such as indium, are sometimes present in small amounts, about 0.1% to 2.0%, as well as some silver. Arsenic is also present in many dusts, and can be found in the range of several percent. This element renders the dust toxic and makes disposal difficult. These metals are present in the form of oxides, sulfides, and sulfates or basic sulfates.
Lead bath treatments are employed for separating metallic lead from other metals such as arsenic, tin, antimony, bismuth, or noble metals. An amount of metallic sodium is added to the lead bath, producing a dross or slag, with the impurities reporting the dross. The dross can then be skimmed off. The purpose here is to improve the purity of the lead bullion. One typical separating process that involves sodium addition to molten lead bullion is described in U.S. Pat. No. 4,404,026.
However, no one has previously found an effective technique to recover the metal value of dusts that may contain indium lead and or arsenic, by subjecting them to a straightforward sodium-charged lead bath.
A technique for recovery of metals, such as indium, from flue dusts that may also contain arsenic, is also described in U.S. Pat. No. 4,244,734. That technique involves a rather complex series of steps based on aqueous, ambient temperature leaching, and involves precipitating the arsenic in the form of an insoluble ferric arsenic compound. The other metals are separated in previous or successive process steps.